The present invention relates to an image forming apparatus for forming an electrostatic latent image by exposing a surface of a photosensitive body by means of an exposing means, and forming an image corresponding to the electrostatic latent image by causing a developer to attach to the electrostatic latent image.
Previously, an image forming apparatus equipped with exposing means for exposing a surface of a photosensitive body to form an electrostatic latent image on the surface of the photosensitive body, and developing means for attaching developer onto the electrostatic latent image to form a developer image corresponding to the electrostatic latent image on the surface of the photosensitive body have been considered. In the image forming apparatus of this type, the image corresponding to the electrostatic latent image can be formed on a recording medium such as paper, or the like by passing the recording medium through a portion opposite to the photosensitive body to transfer the developer image formed on the photosensitive body onto the recorded medium.
However, in the image forming apparatus of this type, a positional relation between a focal point of the exposing means and the surface of the photosensitive body can become displaced from a normal position and thus, light from the exposing means does not focus on the surface of the photosensitive body, and in some cases an isolated dot may disappear or a density in a halftone portion may be increased. Therefore, in the image forming apparatus of the type having a belt that is circulated through the portion opposite to the photosensitive body, the related art proposes that a mark be formed in a halftone on a surface of the belt, then a density of the mark be sensed by a density sensor, and then, based on the sensed result, it be determined whether or not the light from the exposing means is now focused on the photosensitive body.